The United Nations mission in Congo confirmed Wednesday that former Rwandan-backed rebels killed at least 60 civilians and raped dozens more during an attack on an eastern Congolese town in December last year.  The abuses were part of a series of violations carried out by army factions in recent months, highlighting instability ahead of elections, due in just four months time.

United Nations human rights investigators confirmed Wednesday that former Rwandan-backed rebels, now said to be part of Congo's army, killed at least 60 civilians, raped dozens more and burned hundreds of houses in December last year. 

The killings were part of a series of human rights violations carried out by RCD-Goma soldiers during weeks of clashes with pro-government forces in eastern Congo late last year.

Sonia Bakar, the head of the U.N. Congo missions special investigations unit, said Wednesday that two battalions from the former rebel group attacked a pro-government militia in the North Kivu town of Nyabiondo on December 19, killing, raping and pillaging in the process.

The investigator said that although the U.N. mission had shared information with the provincial military authorities during the investigation, no one had been punished for the attacks.

The confirmation of the Nyabiondo attack follows two other investigations by the U.N. mission accusing the former rebels of human rights violations and highlighting the continuing instability in eastern Congo, just four months ahead of planned elections.

Congo is struggling to recover from a five-year war that sucked in six neighboring countries, divided the vast nation and has killed nearly four million people since 1998.

Officially declared over in 2003 when a transitional government of former belligerents was established in the capital, Kinshasa, the conflict still simmers, rendering much of the lawless but mineral-rich east out of government control and reducing prospects for the polls to be held on time.

Underlining the challenges facing those charged with pacifying the lawless east after years of fighting, U.N. investigators previously confirmed two other instances where army factions were responsible for mass human rights violations during the December clashes.

Last month, they said RCD-Goma soldiers had killed at least 30 civilians in summary and systematic executions in an attack on the North Kivu village of Buramba in December last year.

Another investigation said the former rebels and the pro-government forces both committed human rights violations, ranging from the abduction of civilians to carrying out executions in the mining town of Walikale.